Implantable medical device header

ABSTRACT

Techniques for forming a header for an implantable medical device via a two-shot molding process are described. The two-shot molding processes may include a first molding step that creates a first-shot assembly and a second molding step that creates a second-shot assembly. The first-shot assembly may be formed to include one or more protrusions configured to interact with a second-shot mold and/or molding material in the second molding step. The second molding step may be configured to overmold the first-shot assembly. The header may include an attachment plate at least partially embedded in molding material and configured to be mechanically coupled to a body of the implantable medical device.

TECHNICAL FIELD

The disclosure relates to implantable medical devices and, inparticular, to headers for implantable medical devices.

BACKGROUND

Implantable medical devices (IMDs) may be configured to provide one ormore therapies to a patient. For example, an IMD may be implantablewithin the body of a patient to deliver electrical stimulation therapysuch as cardiac stimulation therapy or neurostimulation therapy. Anexample of cardiac stimulation therapy is cardiac pacing, which mayinclude bradycardia pacing, antitachycardia pacing, or cardiacresynchronization therapy. An IMD may that delivers cardiac stimulationtherapy may also provide cardioversion or defibrillation. Examples ofneurostimulation therapy include spinal cord stimulation, deep brainstimulation, gastric stimulation, peripheral nerve stimulation, orpelvic floor stimulation. In other examples, an IMD may be configured todeliver drug therapy to a patient.

In addition to, or instead of delivering therapy, an IMD may beconfigured to sense one or more physiological parameters of a patient.For example, an IMD may be configured to sense various electricalsignals of a patient, such as a cardiac electrogram signal, anelectroencephalogram or other brain signal, or an electromyogram signal.As other examples, an IMD may be configured to sense a cardiovascular orcerebral spinal fluid pressure or flow, heart sounds, patient movementor posture, temperature, blood oxygen saturation, respiration, edema, orpH.

In some examples, an IMD may include a hermetically sealed housing thatencloses internal circuitry such as a hybrid circuit board and one ormore batteries. The IMD may also include a header portion, referred toas a header, which may include an insulating block configured to isolateone or more conductors from each other and the surrounding environment.The header portion may be configured to house one or more components ofthe IMD, such as an antenna or electrode.

SUMMARY

In general, the disclosure is directed to techniques for forming aheader for an implantable medical device via a two-shot molding process.Molding processes described herein may include a first molding step thatcreates a first-shot assembly and a second molding step that creates asecond-shot assembly. The second molding step may be configured toovermold the first-shot assembly. In some examples, the first-shotassembly may be formed to include one or more features configured tointeract with a mold or a molding material in the second molding step.For example, the first-shot assembly may include one or more protrusionscreated by one or more divots of the first-shot mold, and the one ormore protrusions may be particularly configured to perform specificfunctions during the second molding step. The header may also include anattachment plate at least partially embedded in molding material andconfigured to be mechanically coupled to a body of the implantablemedical device.

In one example, the disclosure is directed a method of forming a headerfor an implantable medical device, the method comprising positioning apre-molding assembly within a first-shot mold, wherein the pre-moldingassembly comprises an antenna, an electrode, and an attachment plate,and wherein the first-shot mold defines at least one divot; and creatinga first-shot assembly by introducing a first shot molding material intothe first-shot mold, wherein the first-shot assembly comprises thepre-molding assembly at least partially covered by the first-shotmolding material, wherein the first-shot assembly comprises at least oneprotrusion of the first shot molding material extending from a surfaceof the first-shot assembly and formed by introduction of the first shotmolding material into the at least one divot of the first-shot mold.

In another example, the disclosure is directed to a header for animplantable medical device, the header comprising a first-shot assemblycomprising a pre-molding assembly at least partially covered by amolding material, wherein the pre-molding assembly comprises an antenna,an electrode, and an attachment plate, wherein the first-shot assemblycomprises at least one protrusion of the first shot molding materialextending from a surface of the first-shot assembly and formed byintroduction of the first shot molding material into the at least onedivot of the first-shot mold.

In another example, the disclosure is directed a header for animplantable medical device, the header comprising a header bodycomprising molding material and at least one component within themolding material; and an attachment plate configured to couple theheader to a body of the implantable medical device, wherein theattachment plate comprises a base configured to be mechanically coupledto the body of the implantable medical device, wherein the base definesa space configured to receive at least one feedthrough wire from thebody of the implantable medical device, the at least one feedthroughwire configured to be coupled to the at least one component of theheader body; and at least one extension extending from the base of theattachment plate, wherein the at least one extension defines at leastone void configured to receive a portion of the molding material tocouple the attachment plate to the header body.

In another example, the disclosure is directed to an implantable medicaldevice comprising a header comprising a header body comprising moldingmaterial and at least one component within the molding material, and anattachment plate comprising a base that defines a space, and at leastone extension extending from the base, wherein the at least oneextension defines at least one void configured to receive a portion ofthe molding material to mechanically couple the attachment plate to theheader body, wherein the at least one extension is substantiallyembedded in the molding material; a body comprising electricalcircuitry; and a feedthrough wire positioned through the space definedby the base of the attachment plate, wherein the feedthrough wireelectrically couples the electrical circuitry and the at least onecomponent of the header body, and wherein the base of the attachmentplate is mechanically coupled to the body of the implantable medicaldevice.

In another example, the disclosure is directed to a method comprisingforming a header for an implantable medical device, wherein the headercomprises a header body comprising molding material and at least onecomponent within the molding material, and an attachment platecomprising a base that defines a space, and at least one extensionextending from the base, wherein the at least one extension defines atleast one void configured to receive a portion of the molding materialto mechanically couple the attachment plate to the header body, whereinthe at least one extension is substantially embedded in the moldingmaterial; positioning at least one feedthrough wire through the spacedefined by the base of the attachment plate; electrically coupling theat least one feedthrough wire to the component of the header; andmechanically coupling the base of the attachment plate to the body ofthe implantable medical device, wherein the at least one feedthroughwire is configured to electrically couple electrical circuitry of thebody of the implantable medical device to the component of the header.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages of the disclosure will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example medical devicesystem.

FIG. 2 is a conceptual diagram illustrating an example implantablemedical device of the medical device system of FIG. 1.

FIG. 3 is a schematic perspective diagram of an example header of animplantable medical device (IMD) formed via a two-shot molding process.

FIGS. 4A and 4B are schematic diagrams illustrating an exampleelectrode, antenna, and attachment plate of a header of an IMD.

FIGS. 5A-5D are schematic diagrams illustrating an attachment plate of aheader for an IMD.

FIGS. 6A and 6B illustrate a pre-molding assembly of a header includingan electrode, antenna, and attachment plate.

FIGS. 6C and 6D illustrate a first-shot molding assembly of the header,which may be the pre-molding assembly after a first molding step hasbeen performed.

FIGS. 6E and 6F illustrate a second-shot molding assembly of the header,which may include the first-shot assembly after a second molding stephas been performed.

FIG. 7 is a flow diagram illustrating an example technique for forming aheader for an IMD via a two-shot molding process.

FIG. 8 is a schematic diagram illustrating a pre-molding assemblypositioned within a loading fixture prior to transfer of the pre-moldingassembly into a first-shot mold.

FIG. 9 is another schematic diagram illustrating a pre-molding assemblypositioned within a loading fixture prior to transfer of the pre-moldingassembly into a first-shot mold.

FIG. 10 is a schematic diagram illustrating an example first-shot moldand loading fixture during transfer of a pre-molding assembly from theloading fixture to the first-shot mold.

FIG. 11 is a schematic diagram illustrating a cross-section of thefirst-shot mold and loading fixture of FIG. 10.

FIG. 12 is a schematic diagram illustrating the pre-molding assemblypositioned in the first-shot mold after the loading fixture has beenremoved.

FIG. 13 is a schematic diagram illustrating a cross-section of a moldcavity of the first-shot mold when the pre-molding assembly ispositioned within the mold cavity.

FIG. 14 is a schematic diagram illustrating a first-shot mold whichdefines features configured to create interaction features on thefirst-shot assembly.

FIG. 15 is a schematic diagram illustrating the pre-molding assemblypositioned within the first-shot mold.

FIGS. 16A and 16B are schematic diagrams illustrating the first-shotassembly after the first-shot assembly has been removed from thefirst-shot mold.

FIG. 17 is a schematic diagram illustrating a first-shot assemblypositioned within a second-shot mold.

FIG. 18 is a schematic cross-sectional diagram of the first-shotassembly, including the electrode and a protrusion of the first-shotassembly, positioned within a second-shot mold cavity.

FIG. 19 is a schematic cross-sectional diagram of the first-shotassembly, including a protrusion of the first-shot assembly, positionedwithin a second-shot mold cavity

FIGS. 20A and 20B are schematic diagrams illustrating a second-shotassembly after the second-shot assembly has been removed from thesecond-shot mold.

FIG. 21 is a schematic diagram illustrating an attachment plate of aheader mechanically coupled to a body of an IMD.

FIG. 22 is a flow diagram illustrating an example technique for creatinga header via a two-shot molding process.

FIG. 23 is a flow diagram illustrating another example technique forcreating a header via a two-shot molding process.

FIG. 24 is a flow diagram illustrating an example technique for couplinga header to a body of an implantable medical device.

DETAILED DESCRIPTION

In some examples, components of implantable medical devices (IMDs) maybe formed via molding processes, such as injection molding. In general,injection molding may produce parts from molding material, e.g.,thermoplastic and thermosetting plastic materials. Such material may beforced or allowed to flow into a mold cavity, where the material maycool and harden to the configuration of the cavity, creating a moldedpart.

In the examples described herein, headers for IMDs may be formed viamolding techniques. One or more components, e.g., an antenna, anelectrode, and/or an attachment plate, may be positioned within the moldprior to introduction of the molding material such that the final moldedpart incorporates these components.

The examples described herein utilize two-shot molding processes.Two-shot molding processes use two molding steps to form a molded part,e.g., a molded header for an IMD. In some examples, the second moldingstep may be characterized as an overmold step, such that an assemblyformed in the first molding step is overmolded in the second moldingstep.

In the examples described herein, one or more components of the IMDheader, e.g., an antenna, electrode, and/or an attachment plate, may bepositioned within a loading fixture and transferred to, e.g., loadedinto, a first-shot mold. In some examples, the one or more componentsmay be positioned freely within the first-shot mold, e.g., thecomponents may not be required to be mechanically coupled to one anotherprior to positioning within the first-shot mold. In these examples, thefirst-shot mold may be specifically configured to accommodate theseparate or free components.

In some examples, a first-shot mold configured to receive the freecomponents may reduce the amount of steps required for forming the IMD,by eliminating a step in which the components are mechanically coupledto one another prior to molding. Similarly, positioning the individualcomponents within the first-shot mold without having to mechanicallycouple, e.g., weld, them together beforehand may reduce the amount ofhandling of the components (which may, in some examples, be relativelysmall and delicate) by a user, which can prevent damage to thecomponents.

After the one or more components are positioned within the first-shotmold, molding material may be injected into the first-shot mold tocreate a first-shot assembly that includes one or more featuresconfigured to interact with the second-shot mold or a molding materialin the second molding step. For example, the first-shot assembly mayinclude one or more protrusions extending from a surface of thefirst-shot assembly opposite the electrode and formed by at least onevoid defined within the first shot mold, where the one or moreprotrusions are configured to engage with a wall of the second-shot moldto substantially prevent coverage of the electrode with molding materialduring injection of a second shot molding material into the second-shotmold. In this way, the electrode surface may remain free of material inorder to facilitate efficient and effective sensing and/or therapydelivery via the electrode.

As another example, the first-shot assembly may include one or moreprotrusions extending outward from a surface of the first shot assemblyat a first portion or end of the first-shot assembly, where the one ormore protrusions are configured to guide flow of a second-shot moldingmaterial that is introduced proximate to the first portion or end of thefirst shot assembly in the second-shot mold. More particularly, theprotrusions are configured to guide flow of the second-shot moldingmaterial along a surface of the first-shot assembly, and toward adifferent, second portion or end of the first-shot assembly. The firstportion or end of the first-shot assembly, when positioned within thesecond-shot mold, may be relatively proximate to the location where thesecond-shot molding material is introduced into the second-shot mold.The second portion or end may be less proximate to the location wherethe second shot molding material is introduced into the second shot moldthan the first portion or end. The second portion or end may be oppositethe first portion or end, in some examples. For example, the firstportion or end may be a top portion or end of the first shot assembly,and the second portion or end may be a bottom portion or end of thefirst shot assembly. The first-shot assembly may be positioned into thesecond-shot mold, and the second molding step may subsequently beperformed to overmold the first-shot assembly.

Forming a first-shot assembly that includes one or more protrusionsconfigured to interact with the second-shot mold in the second moldingstep may provide one or more advantages. For example, a first-shotassembly that includes one or more protrusions extending from a surfaceof the first-shot assembly opposite the electrode may allow placement ofthe molding material during the second molding step to be more easilycontrolled, e.g., compared to a conventional overmolding process. Insome examples, placement of the molding material over the first-shotassembly may be confined to particular locations on the first-shotassembly. For example, the one or more protrusions may engage with awall of the second-shot mold to press the electrode against an oppositewall and to substantially prevent coverage of the electrode with moldingmaterial during the second molding step. As another example, afirst-shot assembly that includes one or more protrusions extendingoutward from one portion of the first-shot assembly and configured toguide flow of a second-shot molding material within the second-shot moldalong a surface of the first-shot assembly toward another portion of thefirst-shot assembly may prevent defects, e.g., air bubbles, cracks, andthe like, in the overmold during the second molding step by providing amore extended and continuous flow of the molding material over thefirst-shot assembly.

In some examples, as will be described in further detail below, theattachment plate of the header may be molded into the first-shotassembly and/or the second shot assembly. For example, at least aportion of the attachment plate may be covered by molding material suchthat the attachment plate is mechanically coupled to the header. Theattachment plate may be configured to be mechanically coupled to a canof the IMD, e.g., via laser welding, such that the header ismechanically coupled to the can of the IMD.

FIG. 1 is a conceptual diagram illustrating an example system 10 thatmay be used to monitor one or more physiological parameters of patient14. System 10 includes an implantable medical device (IMD) 16, which iscoupled to programmer 24. IMD 16 may be a subcutaneous sensing deviceconfigured to sense signals indicative of one or more physiologicalparameters of patient 14. For example, IMD 16 may sense and/or storeelectrocardiogram (ECG) signals. In some examples, IMD 16 may beconfigured to sense ECG or other signals and detect arrhythmias, e.g.,ventricular and/or supra-ventricular arrhythmias, based on the signals.

Although the examples described herein include IMD 16 configured tosense physiological signals of patient 14, in other examples IMD 16 mayalternatively or additionally be configured to deliver therapy topatient 14. For example, IMD 16 may be an implantable leadless pacemakerthat provides electrical signals to heart 12 via one or more electrodes(not shown in FIG. 1) on its outer housing. Additionally oralternatively, IMD 16 may sense electrical signals attendant to thedepolarization and repolarization of heart 12 via electrodes on itsouter housing. In some examples, IMD 16 provides therapy to patient 14based on sensed physiological signals. Patient 14 is ordinarily, but notnecessarily, a human patient.

In some examples, IMD 16 may be configured to be implanted proximate toheart 12, e.g., as illustrated in FIG. 1. In other examples, IMD 16 maybe configured to be implanted proximate to or within another portion ofthe body of patient 14.

In the examples described herein, IMD 16 includes a header, which mayinclude one or more components of IMD 16, and may be formed separatelyfrom the rest of IMD 16. In some examples, the header may include anantenna, at least one of the one or more electrodes, and/or anattachment plate configured to attach the header to another portion ofIMD 16. The header may be formed via the molding techniques describedherein.

In the example of FIG. 1, IMD 16 is positioned subcutaneously in a leftpectoral region of patient 14. In other examples, however, IMD 16 may bepositioned within any suitable region of patient 14. In some examples,depending on the location of implant, IMD 16 may include other sensingand/or stimulation functionalities. For example, IMD 16 may provideatrioventricular nodal stimulation, fat pad stimulation, vagalstimulation, or other types of neurostimulation, and/or may sense one ormore parameters of heart 12 or another parameter of patient 12. In someexamples, system 10 may include a plurality of leadless IMDs 16, e.g.,to provide stimulation and/or sensing at a variety of locations.

FIG. 1 further depicts programmer 24 in communication with IMD 16. Insome examples, programmer 24 comprises a handheld computing device,computer workstation, or networked computing device. Programmer 24includes a user interface that presents information to and receivesinput from a user. It should be noted that the user may also interactwith programmer 24 remotely via a networked computing device.

A user, such as a physician, technician, surgeon, electrophysiologist,other clinician, or patient, interacts with programmer 24 to communicatewith IMD 16. For example, the user may interact with programmer 24 toretrieve physiological or diagnostic information from IMD 16. A user mayalso interact with programmer 24 to program IMD 16, e.g., select valuesfor operational parameters of the IMD 16. For example, the user may useprogrammer 24 to retrieve information from IMD 16 regarding the rhythmof heart 12, trends therein over time, or arrhythmic episodes.

IMD 16 and programmer 24 may communicate via wireless communicationusing any techniques known in the art. Examples of communicationtechniques may include, for example, low frequency or radiofrequency(RF) telemetry, proximal inductive interaction, or tissue conductancecommunication, but other techniques are also contemplated. In someexamples, programmer 24 may include a programming head that may beplaced proximate to or in contact with the patient's body near the IMD16 implant site in order to improve the quality or security ofcommunication between IMD 16 and programmer 24.

Although the examples described herein refer to leadless IMD 16, IMD 16may alternatively be coupled to one or more leads comprising one or moreelectrodes configured to sense the one or more physiological parametersof patient 14 and/or to deliver the therapy to heart 12 of patient 14.Additionally, although the examples herein describe monitoringphysiological signals via IMD 16, IMD 16 may additionally oralternatively be configured for pacing therapy for heart 12, neurostimulation therapy, defibrillation therapy, or cardioversion therapyvia one or more electrodes of system 10.

FIG. 2 is a conceptual diagram further illustrating IMD 16. As shown inFIG. 2, IMD 16 may include header 38 coupled to body portion 40. In theexamples described herein, header 38 may include electrode 42, antenna44, and attachment plate 46. In particular, electrode 42, antenna 44,and attachment plate 46 may be molded into header 38 via a two-shotmolding process, as described in further detail below. Body portion 40of IMD 16 may include electrical circuitry 48 and power source 50, insome examples, which may be contained within a hermetic housing or can,e.g., formed of titanium or ceramic.

As shown in FIG. 2, header 38 includes at least one electrode 42.Electrode 42 may be configured to sense physiological signals of patient14 and/or to deliver electrical stimulation therapy to patient 14, e.g.,to treat a cardiac disorder of patient 14. IMD 16 may sense signals ordeliver stimulation via electrode 42 in combination with anotherelectrode, such as the housing of body portion 40. In some examples,electrode 42 may be coated with a material configured to improveperformance, e.g., sensing or pacing performance. For example, electrode42 may be coated with a conductive material such as Titanium Nitride(TiN).

Header 38 also includes antenna 44. Antenna 44 may be configured totransmit and/or receive electromagnetic signals for communication. Forexample, antenna 44 may be configured to transmit to and/or receivesignals from programmer 24. Antenna 44 may be coupled to electricalcircuitry 48 of IMD 16, which may drive antenna 44 to transmit signalsto programmer 24, and may receive signals received from programmer 24via antenna 44. In the example shown in FIG. 2, header 38 additionallyincludes attachment plate 46, which is configured to mechanically coupleheader 38 to body portion 40 of IMD 16, as will be described in furtherdetail below.

In the example shown in FIG. 2, body portion 40 of IMD 16 is configuredto house electrical circuitry 48 and power source 50. Electricalcircuitry 48 may comprise one or more electrical circuits configured toperform any function of IMD 16. For example, the electrical circuitry 48may be coupled to antenna 44 to receive and/or transmit signals.Electrical circuitry 48 may additionally or alternatively be configuredto analyze physiological signals, e.g., signals sensed via electrode 42,and/or to control delivery of stimulation or other therapies. Bodyportion 40 is also configured to house power source 50, which may beconfigured to provide energy to various components of IMD 16, such aselectrical circuitry 48.

FIG. 3 is a schematic perspective diagram of header 38 after a two-shotmolding process, and prior to mechanical and electrical coupling withbody 40 of IMD 16. As shown in FIG. 3, electrode 42, antenna 44, andattachment plate 46 are at least partially molded into header 38. Insome examples, at least a portion of attachment plate 46 andsubstantially entire electrode 42 may not be overmolded with moldingmaterial. Although electrode 42, antenna 44, and attachment plate 46 arevisible in hidden lines in the schematic of FIG. 3, the components maynot actually be visible from an outside view. For example, electrode 42,antenna 44, and attachment plate 46 may be at least partially overmoldedsuch that the components are not entirely visible from an outsideperspective, depending on the opacity of the molding material. The outersurface of header 38 may, in some examples, be relatively smooth andformed of hardened or cured molding material. However, for purposes ofillustration, the components are shown in hidden (e.g., dashed) lines inFIG. 3.

Header 38 may, in some examples, be described herein as including aheader body, which may be any components of header 38 besides attachmentplate 46. For example, the header body of header 38 may includeelectrode 42, antenna 44, components of header 38 coupled to electrode42 and/or antenna 44, molding material that holds the components ofheader 38 together, and the like. Thus, header 38 may include orcomprise a header body and attachment plate 46. For example, as shown inFIG. 3, header 38 may include header body 45 and attachment plate 46.

FIGS. 4A and 4B illustrate electrode 42, antenna 44, and attachmentplate 46 prior to molding, e.g., in a free state. FIG. 4A is atwo-dimensional schematic diagram illustrated in an x-y plane(orthogonal x-y axes are shown for purposes of illustration only), andFIG. 4B is a three-dimensional schematic diagram illustrated in an x-y-zplane (orthogonal x-y-z axes are shown for purposes of illustrationonly).

As shown, electrode 42 may be integral with (e.g., mechanically coupledto) shaft 52, which may be configured to stabilize electrode 42 duringthe molding process. For example, shaft 52 may be configured to interactwith antenna 44, attachment plate 46, and/or one or more components of amolding fixture within which the assembly is placed during molding tostabilize electrode 42 during molding. In addition, shaft 52 may beconfigured to transmit to and receive electrical signals from electrode42 during sensing and/or therapy delivery by IMD 16 after header 38 isincorporated into IMD 16. For example, shaft 52 may be electricallycoupled to electrode 42, in addition to being mechanically coupled toelectrode 42.

Electrode 42 may be formed from any suitable material configured forsensing physiological signals of patient 14 and/or for deliveringelectrical stimulation therapy to patient 14. For example, electrode 42may be formed from titanium or a titanium alloy. In some examples, shaft52 may be formed from the same material as electrode 42 while, in otherexamples, shaft 52 may be formed from a different material. Electrode 42and shaft 52 may be formed from electrically conductive material(s) suchthat electrical signals may be transmitted and received via electrode 42and shaft 52.

Electrode 42 may also have any dimensions suitable for incorporationinto header 38. For example, electrode 42 may be approximately 0.170inches wide (e.g., extending in an x-axis direction) and 0.109 incheslong (e.g., extending in a y-axis direction). Similarly, shaft 52 mayhave any suitable dimensions. For example, shaft 52 may be approximately0.030 inches wide (e.g., extending in an x-axis direction) andapproximately 0.288 inches long (e.g., extending in a y-axis direction).

Antenna 44 may facilitate IMD 16 communications, e.g., communicationswith programmer 24 or other devices. Antenna 44 may be coupled toelectrical circuitry 48, which may include a transmitter and/or receiverto transmit to and/or receive information from one or more otherdevices, such as other devices also implanted within patient 14, orother devices external to patient 14 (e.g., programmer 24). Antenna 44may be configured to improve the ability of IMD 16 to receive and/ortransmit signals, e.g., radio frequency (RF) signals.

In the examples described and illustrated herein, antenna 44 may be athree-dimensional antenna, which may be described as a meandering orserpentine antenna (e.g., in that it includes segments that meander inthree-dimensions). For example, antenna 44 may be a three-dimensionalantenna described in U.S. Patent Application Publication No.2012/0001812 by Zhao et al., entitled “IMPLANTABLE MEDICAL DEVICEANTENNA,” published on Jan. 5, 2012, and incorporated herein byreference in its entirety. In other examples, antenna 44 may haveanother suitable configuration.

Antenna 44 may be described as an antenna that meanders in threedimensions. Antenna 44 may also be described as comprising a serpentinestructure in three dimensions. As shown in FIG. 4B, three-dimensionalantenna 44 includes a plurality of integral segments 54 running paralleland perpendicular to one another such that the segments 54 “meander”from top to bottom of antenna 44, e.g., in a substantially x- toy-direction. (For clarity of illustration, not all segments 54 arelabeled in FIG. 4B). Antenna 44 may be considered to meander in threedimensions (or be considered a three-dimensional serpentine structure),because the individual segments 54 are arranged such that they “meander”between first, second, and third planes of antenna 44.

In one example, a spacing between parallel segments 54 of antenna 44 maybe selected based on a ratio L/2n, where L is a maximum length of avolume of the antenna 44, and n is a number of meandering sections ofantenna 44. In this example, the spacing between parallel segments 54 ofantenna 44 may be constant. In other examples, spacing between segments54 of antenna 44 may be determined in a different manner. In someexamples, the spacing between parallel segments 54 of antenna 44 may notbe selected to be constant.

As shown in FIG. 4B, antenna 44 may additionally include couplingstructure 56 extending downward (e.g., in a substantially negativey-axis direction) from a bottommost segment 54. Coupling structure 56may facilitate electrical connection of antenna 44 to one or more othercomponents, such as electrical circuitry configured to communicatesignals (e.g., electrical circuitry 48 of IMD 16 depicted in FIG. 2). Inthis manner, coupling structure 56 may be considered part of the antennafeed line. Another portion of the antenna feed line may be locatedwithin the housing of the IMD. Coupling structure 56 may, for example,be coupled to one or more other components (e.g., via one or more wires,traces, or other conductive structures) using various mechanisms knownin the relevant art, including for example soldering, conductiveadhesive, and the like. In other examples, coupling structure 56 mayconnect other portions of antenna 44 (e.g., segments other than thebottommost segment 54) to the other components of the IMD.

Antenna 44 may additionally include at least one antenna loadingstructure 58. Antenna loading structure 58 may be coupled to at leastone of the plurality of segments 54. Antenna loading structure 58 isconfigured to provide conductive surface area available for telemetry.For example, the relatively large surface area of antenna loadingstructure may reduce the need for additional segments 54 of antenna 44and, thus, maintain a relatively small size of header 38. The antennaloading structure 58 may also be configured to stabilize impedance ofthe antenna 44 and, thus, reduce the sensitivity of antenna 44 toelectrical noise in the surrounding tissue environments. As anotherexample, antenna loading structure 58 may be configured to provide arelatively large surface for fixation of molding material during thetwo-shot molding process, in comparison to, e.g., thin wires.

As shown in FIGS. 4A and 4B, header 38 also includes attachment plate46, which includes base 60 and extensions 62 which extend outward frombase 60 in a substantially y-axis direction. As will be describedfurther below, base 60 is configured to be mechanically coupled to body40 of IMD 16 to attach header 38 to body 40, and extensions 62 areconfigured to be at least partially covered in molding material duringthe molding process to mechanically couple attachment plate 46 withinheader 38. Header 38 may include a header body portion (e.g., includingsome or all components of header 38 other than attachment plate 46), inaddition to attachment plate 46 configured to mechanically couple header38 to body 40.

FIGS. 5A-5D illustrate various schematic diagrams of attachment plate46. Attachment plate 46 is configured to be partially molded into header38 and to subsequently be mechanically coupled to body 40 of IMD 16. Insome examples, attachment plate 46 is configured to be mechanicallycoupled to body 40 via laser welding.

As mentioned above, attachment plate 46 includes base 60 and one or moreextensions 62 extending from base 60. Extensions 62 are configured to besubstantially molded into header 38 in the first and/or second moldingsteps of the two-shot molding processes described herein. In someexamples, base 60 of attachment plate 46 remains substantially free ofmolding material in order to facilitate mechanical coupling ofattachment plate 46 to body 40.

As shown in FIGS. 5A-5D, extensions 62 of attachment plate 46 may defineone or more voids 63. Voids 63 may be configured to receive moldingmaterial in the first and/or second molding steps in order to create astrong bond of attachment plate 46 to the rest of header 38. Forexample, voids 63 provide space in which molding material cansubstantially surround portions of extensions 62 during molding. In thisway, extensions 62 of attachment plate 46 may become substantiallyembedded within the molding material. Cured molding material positionedwithin voids 63 may withstand substantially more force in comparison tomolding material positioned on a substantially constant surface thatdoes not include voids 63. For example, molding material may becomeenmeshed within voids 63 making it harder to remove from attachmentplate 46 when forces from various directions are applied.

Voids 63 may also function to receive components of a first orsecond-shot mold. For example, voids 63 may be configured to receive oneor more mold cores, e.g., the one or more mold cores may extend throughvoids 63, to stabilize and support distal end 53 of shaft 52 and/orcoupling structure 56 within the first shot mold. In this way, distalend 53 and coupling structure 56 may be prevented from being covered inmolding material during the first molding step. For example, the one ormore mold cores may push against distal end 53 and coupling structure 56to substantially force distal end 53 and coupling structure 56 against awall of a first or second shot mold such that molding material cannotcover distal end 53 and coupling structure 56 during molding. In thisway, distal end 53 and coupling structure 56 may be kept free of moldingmaterial, or “flash free,” during the first molding step. Distal end 53and coupling structure 56 may subsequently be coupled to one or morefeedthrough wires extending from body 40 into header 38 when header 38is coupled to body 40. In other examples, voids 63 may be configured toreceive other suitable types of mold cores, e.g., to stabilize othercomponents of the assembly during molding.

As shown in FIGS. 5A-5D, base 60 of attachment plate 46 also definesspace 65. Space 65 may be configured to receive, from body 40, thefeedthrough wires configured to electrically couple components of body40 of IMD 16 with components of header 38 of IMD 16 upon completion ofheader 38. For example, as shown in FIG. 20, lead extensions orfeedthrough wires may extend upward through space 65 into header 38 toelectrically couple electrical components, e.g., electrical circuitry 48and power source 50, of body 40 with, e.g., distal end 53 and couplingstructure 56.

Attachment plate 46 may be formed from any suitable material(s). Forexample, attachment plate 46 may include titanium or a titanium alloy.

FIGS. 6A and 6B illustrate pre-molding assembly 64, FIGS. 6C and 6Dillustrate first-shot assembly 66, and FIGS. 6E and 6F illustratesecond-shot assembly 68 of a first example header 38. As illustrated inFIGS. 6A and 6B, pre-molding assembly 64 includes electrode 42 (coupledto shaft 52), antenna 44, and attachment plate 46 prior to any moldingsteps. First-shot assembly 66, as shown in FIGS. 6C and 6D, includeselectrode 42 (coupled to shaft 52), antenna 44, and attachment plate 46after a first molding step of a two-shot molding process. As describedherein, first-shot assembly 66 may include one or more featuresconfigured to interact with a second-shot mold during the second moldingstep of the two-shot molding process. Second-shot assembly 68,illustrated in FIGS. 6E and 6F, includes first-shot assembly 66 afterthe second molding step. The second molding step may, in some examples,be described as overmolding the first-shot assembly 66. The second-shotassembly 68 may be the finalized header 38 which may, after thesecond-shot molding step, be ready for coupling to body 40 of IMD 16 viaattachment plate 46.

In some examples, pre-molding assembly 64 may be assembled prior topositioning within a loading fixture, e.g., loading fixture 82 (FIG. 9).For example, a user may arrange electrode 42 (including shaft 52),antenna 44, and attachment plate 46 in a particular configuration priorto positioning the assembly 64 within the loading fixture or othermolding component, e.g., a first-shot mold.

In the example illustrated in FIGS. 6A and 6B, shaft 52 coupled toelectrode 42 is positioned substantially through a middle opening ofantenna 44 defined by segments 54 of antenna 44. A distal end 53 ofshaft 52 (namely an end of shaft 52 positioned away from electrode 42)may be positioned such that the distal end 53 may be electricallycoupled to one or more feedthrough wires or leads of body 40.

In the illustrated example, electrode 42 and antenna 44 are positionedsuch that electrode 42 and antenna loading structure 58 runsubstantially parallel to one another. In some examples, thisconfiguration may provide a surface (e.g., a surface of antenna loadingstructure 58) on which one or more protrusions may be created oppositeelectrode 42 to prevent coverage of electrode 42 with molding materialduring the second molding step, as will be explained in further detailbelow.

As shown in FIGS. 6A and 6B, attachment plate 46 is positioned proximateto the distal end 53 of shaft 52 and a distal end of antenna 44 (e.g.,coupling structure 56), both of which may be coupled to componentswithin body 40 of IMD 16 when header 38 is coupled to body 40.Attachment plate 46 itself may be mechanically coupled to body 40 viaany suitable technique, e.g., laser welding.

In the example illustrated in FIGS. 6A and 6B, electrode 42 and antennaloading structure 58 define grooves 67A and 67B, respectively, which mayprovide space for a suture hole in a finalized header 38. In someexamples, the suture hole may be utilized to suture header 38 to tissuewithin patient 14 such that header 38 and IMD 16 do not migrate from atarget implant site within patient 14. In other examples, IMD 16 mayinclude another type of suitable fixation mechanism to prevent migrationof IMD 16 within tissue of the patient 14.

FIGS. 6C and 6D illustrate first-shot assembly 66. First-shot assembly66 may be formed by performing a first molding step over pre-moldingassembly 64. As shown in FIGS. 6C and 6D, first-shot assembly 66 isformed to include one or more features configured to interact with asecond shot mold or molding material during a second molding stepsubsequent to the first molding step. In particular, in the exampleassembly 66 illustrated in FIGS. 6C and 6D, assembly 66 includesprotrusions 70A, 70B and protrusions 72A, 72B. In addition, first-shotassembly 66 includes suture-hole groove 69, created by grooves 67A, 67Bof pre-molding assembly 64, which is configured to form a suture hole inthe second-shot assembly 68, as shown in FIGS. 6E and 6F.

Protrusions 70A, 70B may be formed by first and second divots,respectively, defined within the first-shot mold. The first and seconddivots may be defined within the first-shot mold such that, whenpre-molding assembly 64 is positioned within the first-shot mold, thefirst and second divots are positioned proximate to a surface ofpre-molding assembly 64 opposite electrode 42 (e.g., proximate toantenna loading structure 58). In this way, when the first-shot moldingmaterial enters the first and second divots, protrusions 70A, 70B areformed by the first and second divots and extend from the surface of thefirst-shot assembly 66 opposite electrode 44. Protrusions 70A, 70B offirst-shot assembly 66 may be configured to engage with a wall of thesecond-shot mold to substantially prevent coverage of electrode 42during injection of the second-shot molding material into thesecond-shot mold. For example, protrusions 70A, 70B may engage with thewall of the second-shot mold to compress first-shot assembly 66 withinthe second shot mold such that the outer surface of electrode 42 isfirmly pressed against a wall of the second-shot mold proximate theelectrode 42.

Although FIGS. 6C and 6D illustrate two protrusions 70A, 70B, in otherexamples, first-shot assembly 66 may include more or less than twoprotrusions extending from a surface of the first-shot assembly 66opposite electrode 42. In these examples, the first-shot mold mayinclude any suitable number of divots configured to receive thefirst-shot molding material and form the one or more protrusions 70extending from the surface of the first-shot assembly 66.

As shown in FIGS. 6C and 6D, first-shot assembly 66 also includesprotrusions 72A and 72B extending outward from a surface at a firstportion or end of the first-shot assembly. In this way, protrusions 72A,72B may be configured to guide flow of a second shot molding materialthat is introduced proximate to the first portion or end of thefirst-shot assembly 66 in the second-shot mold. For example, moldingmaterial may be introduced into a mold cavity of the second-shot moldproximate to the end of first-shot assembly 66 that includes protrusions72A, 72B. Protrusions 72A, 72B may be configured to guide flow of thesecond-shot molding material toward a different, second portion or endof first-shot assembly 66.

In some examples, first-shot assembly 66 may define a longitudinal axisthat extends between the first and second ends of the first-shotassembly 66. The first end of first-shot assembly 66, on whichprotrusions 72A, 72B are formed, may be a portion of first-shot assembly66 proximate to electrode 42 and/or antenna loading structure 58, insome examples. The first end or portion of first-shot assembly 66 may,in some examples, be referred to as a substantially top portion offirst-shot assembly 66. The second end or portion of first-shot assembly66, toward which protrusions 72A, 72B may guide molding material in thesecond shot mold, may be a portion or end of first-shot assembly 66proximate to attachment plate 46 and/or distal end 53 of shaft 52 and/orantenna coupling structure 56, in some examples. The second end orportion of first-shot assembly 66 may, in some examples, be referred toas a substantially bottom portion of first-shot assembly 66.

In the example illustrated in FIGS. 6C and 6D, the protrusions 72A, 72Bare positioned proximate to electrode 42 and antenna loading structure58 and extend between electrode 42 and antenna loading structure 58,e.g., in a substantially transverse direction relative to thelongitudinal axis 73 of the header in FIGS. 6C, 6D. Protrusions 72A, 72Bmay be configured to direct or guide flow of molding material along asurface of the first-shot assembly from a first portion or end of thefirst-shot assembly 66 toward a second portion or end of the first-shotassembly 66 within the second-shot mold during the second molding step.

In some examples, protrusions 72A, 72B may be defined by a particularshape, contour, texture, or other characteristic that is configured todirect or guide flow of the molding material during the second moldingstep in a particular manner. For example, protrusions 72A, 72B may berelatively smooth such that molding material may flow around theprotrusions from the first portion of the first-shot assembly 66 to thesecond portion of the first-shot assembly 66. The protrusions 72A, 72Bmay, in some examples, be rounded to facilitate flow of the moldingmaterial through the second shot mold.

In some examples, features of the first-shot mold may create one or moreopen regions 71 in the first-shot assembly 66, e.g., regions that didnot fill with molding material in the first molding step. For example,as illustrated in FIG. 13, alignment features 100 and support features101 extend into pre-molding assembly 64 within the first-shot mold, suchthat molding material may not enter the spaces occupied by features 100and 101 in the first molding step. The spaces occupied by features 100and 101 in the first molding step may, thus, define open regions 71 inthe first-shot assembly 66.

Protrusions 72A, 72B may be configured to direct molding material in thesecond molding step through open regions 71 by guiding the moldingmaterial in a particular manner. In some examples, protrusions 72A, 72Bcontact walls of the second shot mold to keep first-shot assembly 66central during the second molding step and to block flow of the moldingmaterial from moving in a particular direction during the second moldingstep, e.g., to prevent entrapment of air within the molding material.

As an example, protrusions 72A, 72B may be configured to engage withwalls of the second shot mold to stabilize first-shot assembly 66 in acentral position within the second shot mold. Protrusions 72A, 72B mayengage with the walls of the second shot mold such that molding materialis initially prevented from moving along the sides of first-shotassembly 66 and directly into regions 71, and instead is substantiallyforced along the plane of pre-molding assembly 66 that is proximate toantenna loading structure 58 and protrusions 70A, 70B. The moldingmaterial may subsequently enter regions 71 after moving along the planeof pre-molding assembly 66 that is proximate to antenna loadingstructure 58. Guidance of molding material by protrusions 72A, 72Bduring the second molding step will be described in further detail withrespect to FIG. 19.

As with protrusions 70A and 70B, protrusions 72A and 72B may be formedby two divots defined within the first-shot mold. In the exampleillustrated in FIGS. 6A-6D, the divots may be defined within thefirst-shot mold such that, when pre-molding assembly 64 is positionedwithin the first-shot mold, the two divots are positioned proximate toand extending between electrode 42 and antenna loading structure 58 onthe sides of pre-molding assembly 64. In this way, when the first-shotmolding material enters the divots, protrusions 72A, 72B are formed on asubstantially top portion of first-shot assembly 66, e.g., proximate toand extending between electrode 42 and antenna loading structure 58. Asdiscussed above, protrusions 72A, 72B may be configured to guide moldingmaterial from a substantially top portion toward a substantially bottomportion of the first-shot assembly 66 within the second-shot mold, e.g.,to provide substantially even coverage of first-shot assembly 66 withmolding material and/or to prevent defects within the cured second shotmolding material.

Although FIGS. 6C and 6D illustrate two protrusions 72A, 72B, in otherexamples, first-shot assembly 66 may include more or less than twoprotrusions extending from a substantially top portion of the first-shotassembly. In these examples, the first-shot mold may include anysuitable number of divots configured to receive the first-shot moldingmaterial and form the one or more protrusions 72.

FIGS. 6E and 6F illustrate second-shot assembly 68, which may also bereferred to as header 38. That is, second-shot assembly 68 may be thefinalized header 38. Second-shot assembly 68 is formed by performing asecond molding step over first-shot assembly 66, e.g., an overmoldingstep, within a second-shot mold. In the examples illustrated in FIGS. 6Eand 6F, second-shot assembly 68 may define suture hole 74, which may beformed within the space defined by suture-hole groove 69 during thesecond molding step.

As illustrated in FIGS. 6E and 6F, the second molding step may leave oneor more components of second-shot assembly 68 exposed. For example, inthe example illustrated in FIGS. 6E and 6F, electrode 42, distal end 53of shaft 52 (which may be integral with electrode 42), and base 60 ofattachment plate 46 may not be overmolded in the second molding step.Electrode 42 may be kept free of molding material (e.g., “flash” free)such that electrode 42 may clearly sense physiological signals and/ordeliver stimulation therapy when IMD 16 is implanted within a patient.Distal end 53 of shaft 52 may be kept free of molding material such thatdistal end 53 of shaft 52 may be electrically coupled to one or morefeedthrough wires or leads from body 40 to electrically couple electrode42 to electrical components of body 40. Similarly, although not shown inFIGS. 6E and 6F, antenna coupling structure 56 may also be kept free ofmolding material in order to facilitate electrical coupling with wiresor leads from body 40 to electrically couple antenna 44 to electricalcomponents of body 40. Base 60 of attachment plate may be kept free ofmolding material in order to facilitate mechanical coupling ofattachment plate 46 (and, consequently, header 38) to body 40 of IMD 16.

FIG. 7 is a flow diagram illustrating an example technique for formingheader 38 via a two-shot molding process. According to the techniqueillustrated in FIG. 7, pre-molding assembly 64 (e.g., electrode 42 andshaft 52, in examples in which electrode 42 is integral with shaft 52,antenna 44, and attachment plate 46) is positioned within a first-shotmold (76). In some examples, pre-molding assembly 64 may be positionedwithin the first-shot mold via a loading fixture, as will be describedin greater detail with respect to FIGS. 8-11. In some examples, theloading fixture may comprise one or more components configured to alignand/or constrain the electrode 42, antenna 44, and attachment plate 46in a particular configuration relative to one another. The loadingfixture may interface with a molding cavity of the first-shot mold, andthe pre-molding assembly 64 may be aligned within a cavity of thefirst-shot mold and transferred from the loading fixture to thefirst-shot mold. The loading fixture may be removed after thepre-molding assembly 64 is positioned within the first-shot mold andbefore a first-shot molding material is injected into the first-shotmold.

According to the technique illustrated in FIG. 7, after positioning ofthe pre-molding assembly 64 within the first-shot mold, a first shotmolding material is injected into the first-shot mold to at leastpartially cover the pre-molding assembly 64 and to create one or moreprotrusions on the first-shot assembly 66 (78). For example, asdescribed above, the first-shot mold may include one or more divotsconfigured to receive molding material during the first molding stepsuch that, when the molding material has hardened, first-shot assembly66 includes one or more protrusions (e.g., protrusions 70A, 70B, 72A,72B) configured to interact with a second-shot mold and/or second-shotmolding material.

The first-shot molding material may be any suitable molding material.For example, the first-shot molding material may be a thermoplasticmaterial, such as medical grade polyurethane. In some examples, thematerial may have a durometer of between approximately 50 and 90 on ashore D scale. The molding material may, in some examples, be heated toapproximately 450 degrees Fahrenheit and injected into a molding cavitywhich is relatively cooler, e.g., approximately 85 degrees Fahrenheit.The molding material may harden on contact with the relatively coolermolding cavity, thus hardening before being ejected out of the cavity.

According to the technique shown in FIG. 7, upon creating the first-shotassembly 66 including the protrusions (e.g., protrusions 70A, 70B and/orprotrusions 72A, 72B), the first-shot assembly 66 may be positionedwithin a second-shot mold (79). In some examples, a loading fixture maybe used to position the first-shot assembly 66 within the second-shotmold, while, in other examples, a loading fixture may not be used. Afterthe first-shot assembly 66 is positioned within the second-shot mold, asecond-shot molding material is injected into a second-shot mold to atleast partially overmold the first-shot assembly 66 (80). As describedwith respect to FIGS. 6E and 6F, various components of the second-shotassembly 68 may not be overmolded during the molding process. That is,they may be kept free of molding material. For example, electrode 42 maynot be covered by molding material during the second molding step, e.g.,may be kept “flash free”. In this way, electrode 42 may be able to senseand/or deliver therapy via electrode 42 after the header 38 is formed.After hardening or curing of the second-shot molding material, header 38may be substantially complete and ready for mechanical coupling to body40 of IMD 16.

The second-shot mold may include various features configured to interactwith the interaction features created on the first-shot mold. Forexample, in examples in which the interaction features are protrusions70A, 70B configured to engage with a surface of the second-shot mold toprevent coverage of electrode 42 with molding material, the second-shotmold may include a surface proximate to a surface of the first-shotassembly that is opposite the electrode 42 (e.g., a surface proximate toantenna loading structure 58) such that the protrusions 70A, 70B mayengage with the surface of the second-shot mold.

In some examples, the second-shot mold may be a different mold than thefirst-shot mold. In these examples, prior to injection of thesecond-shot molding material into the second-shot mold, the first-shotassembly may be moved and positioned within the second-shot mold. Insome examples, a second loading fixture may be utilized to transfer thefirst-shot assembly 66 to the second-shot mold.

The second-shot molding material may be any suitable molding material.For example, the second-shot molding material may be a thermoplasticmaterial, such as a medical grade polyurethane. In some examples, thematerial may have a durometer of between approximately 50 and 90 on ashore D scale. The molding material may, in some examples, be heated toapproximately 450 degrees Fahrenheit and injected into a molding cavitywhich is relatively cooler, e.g., approximately 85 degrees Fahrenheit.The molding material may harden on contact with the relatively coolermolding cavity, thus hardening before being ejected out of the cavity.

FIG. 8 is a schematic diagram illustrating pre-molding assembly 64(FIGS. 6A, 6B) positioned within loading fixture 82 prior to the firstmolding step of the two-shot molding process. Loading fixture 82 isconfigured to align pre-molding assembly 64 (e.g., to align theindividual components of pre-molding assembly 64) such that pre-moldingassembly 64 may be transferred to first-shot mold 90 in an appropriateconfiguration (FIG. 10).

As shown in FIG. 8, the components of pre-molding assembly 64 may bepositioned and secured/stabilized on loading fixture 82. Loading fixture82 may include predefined alignment features configured to receive thecomponents of pre-molding assembly 64 and maintain alignment of thecomponents during transfer to the first-shot mold 90. In some examples,loading fixture 82 may be formed such that the components of assembly 64are held in place within loading fixture 82 by gravity, prior totransfer of the components to first-shot mold 90. For example, loadingfixture 82 may include one or more grooves or alignment features withinwhich the components of assembly 64 may be positioned or loaded, asshown in more detail in FIG. 9.

Loading fixture 82 is configured to interface with first-shot mold 90 totransfer pre-molding assembly 64 to first-shot mold 90. For example,loading fixture 82 may include pins 86 extending from a surface ofloading fixture 82 and configured to engage with first-shot mold 90 tosubstantially secure first-shot mold 90 and loading fixture 82 to oneanother during transfer of assembly 64 to first-shot mold 90. The pins86 may align with corresponding holes in the first-shot mold 90 tosecure the mold 90 and loading fixture to one another. Although FIG. 8illustrates pins 86 configured to engage with first-shot mold 90, inother examples first-shot mold 90 may include any mechanism suitable foraligning and/or mechanically coupling loading fixture 82 with first-shotmold 90.

In the example shown in FIG. 8, mold pickout 84 may be positioned over aportion of pre-molding assembly 64. Mold pickout 84 may be configured tosubstantially cover particular portions of pre-molding assembly 64during the first molding step to prevent molding material fromcontacting the covered portions of assembly 64. For example, moldpickout 84 may be configured to cover base 60 of attachment plate 46,antenna coupling structure 56 of antenna 44, and distal end 53 of shaft52 during the first molding step. In this way, base 60, antenna couplingstructure 56, and distal end 53 may remain free of molding materialduring the first molding step. Mold pickout 84 may be aligned in loadingfixture 82 and subsequently transferred to first-shot mold 90 along withpre-molding assembly 64.

FIG. 9 is a schematic diagram illustrating assembly 64 positioned withinloading fixture 82. Loading fixture 82 may comprise any componentssuitable for aligning electrode 42, shaft 52, antenna 44, and attachmentplate 46 substantially freely within loading fixture 82. For example,loading fixture 82 may facilitate positioning of the components ofassembly 64 within loading fixture 82 without requiring mechanicalcoupling of the components to one another prior to loading into loadingfixture 82.

In the example shown in FIG. 9, loading fixture 82 includes alignmentfeatures 88 which define cavities within which antenna 44 or, moreparticularly, segments 54 of antenna 44, may be positioned. For example,depending upon the dimensions and configuration of antenna 44, loadingfixture 82 may be formed to include cavities which line up with and arethus configured to receive various portions and/or segments of antenna44, as shown in FIG. 9.

In some examples, loading fixture 82 also includes stabilizing structure89 configured to stabilize electrode 42 and antenna loading structure 58of antenna 44 within loading fixture 82. As shown in FIG. 9, stabilizingstructure 89 is configured to engage grooves 67A, 67B of pre-moldingassembly 64 to substantially prevent motion (e.g., side-to-side motion)of electrode 42 and antenna loading structure 58. In particular, in theexample of FIG. 9, stabilizing structure 89 is positioned within grooves67A, 67B to stabilize pre-molding assembly 64 within loading fixture 82.

FIG. 10 is a schematic diagram illustrating an example first-shot mold90 and loading fixture 82 during transfer of assembly 64 to first-shotmold 90. As illustrated in FIG. 10, loading fixture 82 is configured toengage with first-shot mold 90 during transfer of pre-molding assembly64 to first-shot mold 90. For example, loading fixture 82 may includepins 86 (FIG. 8) which are configured to be positioned within one ormore cavities (not shown) defined within first-shot mold 90 tosubstantially align loading fixture 82 with first-shot mold 90 in themanner illustrated in FIG. 10. Pins 86 and the cavities defined withinfirst-shot mold 90 may be positioned such that, when pins 86 areinserted into the cavities, the pre-molding assembly 64 is aligned witha molding cavity of the first-shot mold 90. The pre-molding assembly 64may subsequently be transferred into the molding cavity of thefirst-shot mold 90.

FIG. 11 is a schematic diagram illustrating a cross-section of theassembly shown in FIG. 10. In particular, FIG. 11 illustrates assembly64 (including electrode 42, antenna 44, and attachment plate 46)positioned within loading fixture 82 when loading fixture 82 is engagedwith first-shot mold 90 prior to full transfer of assembly 64 tofirst-shot mold 90. Loading fixture 82 is configured to interface withfirst-shot mold 90 to guide assembly 64 into a constrained positionwithin first-shot mold 90.

Loading fixture 82 and first-shot mold 90 may interface in any mannersuitable to transfer pre-molding assembly 64 from loading fixture 82 tofirst-shot mold 90.

FIG. 12 illustrates pre-molding assembly 64 positioned in first-shotmold 90 after loading fixture 82 has been removed. In the exampleillustrated in FIG. 12, first-shot mold 90 includes cams 92 configuredto hold or maintain pre-molding assembly 64 in place while loadingfixture 82 is removed, e.g., when pre-molding assembly 64 is transferredfrom loading fixture 82 to first-shot mold 90. In particular, cams 92may engage with pre-molding assembly 64 (e.g., via one or more alignmentfeatures, not shown in FIG. 12) while pre-molding assembly 64 ispositioned within loading fixture 82 and may hold pre-molding assembly64 within first-shot mold 90 while loading fixture 82 is removed.

As shown in FIG. 12, mold pickout 84 may also be transferred fromloading fixture 82 to first-shot mold 90, in some examples. In this way,mold pickout 84 may keep one or more components of pre-molding assembly64 free and clear of molding material during the first molding step ofthe two-shot molding process.

First-shot mold 90 also includes molding material distributor 94, whichmay be configured to deliver first-shot molding material into the moldcavity 98 (FIG. 13) of first-shot mold 90. Distributor 94 may beconnected to the mold cavity 98 via connectors 96 (shown in FIG. 14),through which distributor 94 may deliver the first-shot molding materialinto the mold cavity 98.

FIG. 13 is a schematic diagram illustrating a cross-section of moldcavity 98 of first-shot mold 90 when pre-molding assembly 64 ispositioned within mold cavity 98. As illustrated in FIG. 13, first-shotmold 90 may include alignment features 100 configured to stabilize andalign pre-molding assembly 64 within mold cavity 98. In particular,alignment features 100 may be configured to extend between segments ofantenna 44 to stabilize antenna 44 within mold cavity 98. In someexamples, stabilization of antenna 44 via alignment feature 100 mayresult in stabilization of other components of pre-molding assembly 64within cavity 98 because the components of pre-molding assembly 64 maysupport one another. In some examples, the alignment features 100 may beintegral with cams 92. In the example illustrated in FIG. 13, first-shotmold 90 also includes support features 101 configured to support shaft52 within cavity 98. In some examples, alignment features 100 and/orsupport features 101 may create open regions 71 (FIGS. 6C, 6D) withinfirst-shot assembly 66.

FIG. 14 is a schematic diagram illustrating first-shot mold 90, whichdefines divots configured to create protrusions on first-shot assembly66. For example, in the example illustrated in FIG. 14, first-shot mold90 includes divots 102 configured to create protrusions 70A, 70B onfirst-shot assembly 66 and divots 104 configured to create protrusions72A, 72B on first-shot assembly 66. As described above, the protrusions70A, 70B may be configured to interact in a particular manner with thesecond-shot mold during the second step of the two-shot molding processand the protrusions 72A, 72B may be configured to interact in aparticular manner with molding material during the second step of thetwo-shot molding process.

As illustrated in FIG. 14, first-shot mold 90 may define divots 102configured to receive molding material to create protrusions 70A, 70B onfirst-shot assembly 66. Divots 102 may be defined within first-shot mold90 proximate to a side of pre-molding assembly 64 opposite electrode 42.In the examples described herein, divots 102 are positioned proximate toa side of pre-molding assembly 64 that includes antenna loadingstructure 58 (which is positioned opposite electrode 42 in the examplesdescribed herein).

As illustrated in FIG. 14, first-shot mold 90 may also define divots 104configured to receive molding material to create protrusions 72A, 72B onfirst-shot assembly 66. Divots 104 may be defined within first-shot mold90 proximate to a substantially top portion of pre-molding assembly 64.In particular, divots 104 may be defined within first-shot mold 90 suchthat, when pre-molding assembly 64 is positioned within first-shot mold90, divots 104 extend between electrode 42 and antenna loading structure58. In this way, when molding material fills divots 104 during afirst-shot molding step, protrusions 72A, 72B may be created on asubstantially top portion of first-shot assembly 66. As discussed above,protrusions 72A, 72B may be configured in a particular manner to guideflow of molding material from a substantially top portion of first-shotassembly 66 to a substantially bottom portion of first-shot assembly 66within a second shot mold. Divots 104 of first-shot mold 90 may reflecta desired configuration of protrusions 72A, 72B, e.g., may define aparticular shape, texture, or other characteristics reflective offunction of guiding flow of the molding material during the secondmolding step.

FIG. 15 is another schematic diagram illustrating pre-molding assembly64 positioned within first-shot mold 90. As illustrated in FIG. 15,portion 102 comprises feature 108. Feature 108 may be configured tocreate suture-hole groove 69 on first-shot assembly 66. For example,molding material may form to the shape of feature 108 proximate toantenna loading structure 58 and electrode 42 to create the indentationssuture-hole groove 69.

In addition, divots 102 and 104 are also visible in the schematic ofFIG. 15, proximate to antenna loading structure 58. Divots 102 areconfigured to receive molding material during the first molding step tocreate protrusions 70A, 70B on the surface of first-shot assembly 66proximate to antenna loading structure 58 and opposite electrode 42.Divots 104 are configured to receive molding material during the firstmolding step to create protrusions 72A, 72B extending outward from asubstantially top portion of the first-shot assembly 66. During thefirst molding step, molding material may fill divots 102 and 104 and,upon hardening, may create the protrusions 70A, 70B and 72A, 72B on thefirst-shot assembly 66.

FIGS. 16A and 16B illustrate first-shot assembly 66 after the firstmolding material has been injected into the first-shot mold 90, thefirst molding material has been cured/hardened, and the first-shotassembly 66 has been removed from the first-shot mold 90. As shown inFIGS. 16A and 16B, first-shot assembly 66 defines protrusions 70A, 70Band 72A, 72B and suture-hole groove 69. As illustrated, protrusions 70A,70B extend from a surface of first-shot assembly 66 that is oppositeelectrode 42, and protrusions 72A, 72B extend outward from asubstantially top portion of first-shot assembly 66. As discussed above,protrusions 70A, 70B facilitate keeping electrode 42 free of moldingmaterial (e.g., “flash free”) during a second molding step, andprotrusions 72A, 72B are configured to guide flow of molding materialduring the second molding step.

FIG. 17 is a schematic diagram illustrating first-shot assembly 66positioned within second-shot mold 110. First-shot assembly 66 may beremoved from first-shot mold 90 after the first molding step iscomplete, and may be subsequently positioned into second-shot mold 110for a second molding step, as shown in FIG. 17. In some examples, thesecond molding step may be considered an “overmold” step in that thesecond step may provide a second layer of molding material over at leastpart of the first-shot assembly to complete header 38. As illustrated inFIG. 17, second-shot mold 110 is coupled to distributor 111, which isconfigured to distribute molding material into the cavity of second shotmold 110 during the second molding step.

FIG. 18 is a schematic cross-sectional diagram of first-shot assembly66, including electrode 42, shaft 52, and protrusion 70A (protrusion 70Bis not shown in the cross-section of FIG. 18), positioned withinsecond-shot mold cavity 116 defined within second-shot mold 110. Antenna44 is not shown in the cross-section of FIG. 18, for purposes ofclarity. In the example illustrated in FIG. 18, second-shot mold 110includes opposing walls 118 and 120 (e.g., walls 118 and 120 may beconsidered opposite one another). Wall 118 may also be characterized asbeing proximate to protrusions 70A, 70B and opposite (e.g., on anopposite side of mold 116) electrode 42; similarly, wall 120 may becharacterized as being proximately to electrode 42 and oppositeprotrusions 70A, 70B. As illustrated in FIG. 16A, protrusions 70A, 70B(70B not shown in the cross-section of FIG. 18) are configured to engagewith wall 118 to substantially press electrode 42 against wall 120. Inthis way, molding material may be prevented from covering electrode 42because there is no space between electrode 42 and wall 120 into whichmolding material can enter. Because electrode 42 is pressed against wall120, electrode 42 may not be covered with molding material duringinjection of molding material into second-shot mold cavity 116, thuskeeping electrode 42 free of molding material, or “flash free.” Uponcompletion of header 38, an outer surface of electrode 42 may be clearand able to sense physiological signals and/or deliver therapy.

FIG. 19 is another cross-sectional schematic diagram of first-shotassembly 66 positioned within second-shot mold cavity 116. FIG. 19illustrates protrusion 72A, which is configured to guide the flow ofmolding material during the second molding step. (Protrusion 72B is notvisible in the cross section of FIG. 19.) The arrows shown in FIG. 19illustrate the flow of molding material after it is introduced intosecond-shot mold cavity 116 through distributor 111.

In the example illustrated in FIG. 19, protrusion 72A extends betweenelectrode 42 and antenna coupling structure 58 (not shown). Protrusion72A is configured to engage with wall 120 of second-shot mold 110 and awall of second-shot mold 110 that is substantially perpendicular to wall120 and substantially parallel to the page of FIG. 19. In this way,protrusion 72A may substantially create a seal such that moldingmaterial is initially prevented from flowing along or proximate to wall120 from the first end of mold cavity 116 proximate to the distributor11 to the second end of mold cavity 116. That is, protrusion 72Asubstantially blocks the molding material exiting distributor 111 fromtraveling along wall 120 initially. Protrusion 72A may substantiallyforce the molding material to instead travel along wall 118 and moveover to travel along wall 120 within regions 71 (between segments 54 ofantenna 44), instead of initially traveling along wall 120 when it isintroduced into mold cavity 116.

In the example illustrated in FIG. 19, molding material travels fromdistributor 111 into a first end or portion of mold cavity 116, travelsalong protrusion 72A toward wall 118, and travels downward within moldcavity 116 between wall 118 and a surface of first-shot assembly 66proximate to antenna loading structure and opposite electrode 42. Themolding material then travels toward wall 120 of mold cavity 116 throughregions 71 in a single direction (e.g., toward wall 120). The moldingmaterial may then travel from a first end of cavity 116 proximate todistributor 111 to a second end of cavity 116 away from distributor 111along both walls 120 and 118.

The configuration illustrated in FIG. 19 may have one or moreadvantages. For example, protrusion 72A may force molding material totravel in only one direction within regions 71 because molding materialis entering the cavity only along wall 118, which may prevent thecreation of air bubbles within the molding material within regions 71.For example, if the molding material were to enter regions 71 from twodirections (e.g., moving toward wall 118 and toward wall 120) such thatthe fronts of molding material would meet substantially in the middle ofregions 71, air may be trapped and air bubbles may be created at thelocation where the two fronts meet. Air bubbles in the molding materialmay, in some examples, create regions in which the molding material ismore fragile, less structurally sound, etc. Thus, protrusions 72A, 72Bconfigured to guide the flow of molding material in the mannerillustrated in FIG. 19 may prevent entrapment of air bubbles in themolding material of header 38.

FIGS. 20A, 20B illustrate second-shot assembly 68, or header 38, afterassembly 68 has been removed from the second-shot mold 110 (after thesecond molding step). As illustrated, second-shot assembly 68 includesovermold 122, which may be a layer of cured molding material, over thefirst-shot assembly 66. As shown in FIG. 20A, distal end 53 of shaft 52and antenna coupling structure 56 are exposed and free of moldingmaterial in assembly 68. Thus, distal end 53 and structure 56 may beelectrically coupled to feedthrough wires of body 40 of IMD 16 tofacilitate transmission of electrical signals between header 38 and body40 (e.g., electrical circuitry 48 of body 40). In addition, as shown inFIGS. 20A, 20B, base 60 of attachment plate 46 may also be exposed andfree of molding material such that base 60 may be mechanically coupled(e.g., laser welded) to body 40 of IMD 16. As shown in FIG. 20B,electrode 42 is also exposed and free of molding material in assembly68, such that electrode 42 may sense physiological signals and/ordeliver electrical stimulation therapy to patient 14.

FIG. 21 is a schematic diagram illustrating attachment plate 46 coupledto body 40 of IMD 16. In the diagram shown in FIG. 21, other componentsof header 38 are not included, for clarity of illustration; however,header 38 as a whole may be mechanically and electrically coupled tobody 40 of IMD 16.

As illustrated in FIG. 21, base 60 of attachment plate 46 may bemechanically coupled to body 40. For example, base 60 of attachmentplate 46 may be laser welded to body 40 of IMD 16 to mechanicallycoupled header 38 to body 40. In other examples, base 60 of attachmentplate 46 may be mechanically coupled to body 40 using another suitabletechnique.

As shown in FIG. 21, space 65 (FIGS. 5A, 5D) defined within base 60 ofattachment plate 46 is configured to accommodate or receive feedthroughwires 124 and 126 which extend upward into space 65 from body 40.Feedthrough wires 124 and 126 may extend to electrical circuitry withinbody 40, e.g., electrical circuitry 48, and may be configured to beelectrically coupled to antenna 44 and electrode 42, respectively. Forexample, feedthrough wire 124 may be electrically coupled to antennacoupling structure 56 in order to facilitate communications of IMD 16via antenna 44, e.g., with programmer 24. Similarly, feedthrough wire126 may be electrically coupled to distal end 53 of shaft 52 (whichextends to electrode 42) in order to facilitate control of electrode 42,e.g., sensing and/or therapy delivery, by a component of body 40, suchas a processor. In this way, header 38 (or second-shot assembly 68) maybe mechanically and electrically coupled to body 40 of IMD 16.

FIG. 22 is a flow diagram illustrating an example technique for creatingheader 38 that includes creating a first-shot assembly with one or moreprotrusions configured to engage with a wall of a second-shot moldopposite electrode 42 during a second molding step of a two-shot moldingprocess. According to the technique of FIG. 22, pre-molding assembly 64may be positioned within first-shot mold 90 (128). In some examples, asdescribed above with respect to FIGS. 8-11, a loading fixture, e.g.,loading fixture 82, may be utilized to align and transfer pre-moldingassembly 64 to first-shot mold 90.

In some examples, first-shot mold 90 may include divots 102 (FIGS. 14,15) configured to form protrusions 70A, 70B on first-shot assembly 66after the first molding step. Thus, positioning of pre-molding assembly64 within first-shot mold 90 may, in some examples, include aligningpre-molding assembly 64 within first-shot mold 90 such that divots 102are positioned proximate to a particular portion of pre-molding assembly64, e.g., proximate to a surface of pre-molding assembly 64 oppositeelectrode 42, such as proximate to antenna loading structure 58, in theexamples described herein.

After positioning of pre-molding assembly 64 within first-shot mold 90,a first shot of molding material may be injected into first-shot mold 90to at least partially cover pre-molding assembly 64 and to createprotrusions 70A, 70B on first-shot assembly 66 (130). After thefirst-shot molding material has been cured and/or hardened, thefirst-shot assembly 66 may be removed from the first-shot mold andtransferred to a second-shot mold 110. In some examples, the first-shotassembly 66 may be transferred to second-shot mold 110 via a secondloading fixture.

First-shot assembly 66 may be positioned within second-shot mold 110. Inparticular, according to the example technique of FIG. 22, first shotassembly 66 may be placed within first-shot mold 90 by placingprotrusions 70A, 70B against wall 118 (FIG. 18) of second-shot mold 110,which is opposite electrode 42 (132). In this configuration, protrusions70A, 70B press against wall 118 and, thus, apply pressure to electrode42 to press electrode 42 against wall 120. In this way, molding materialis prevented from covering electrode 42 and, thus, electrode 42 remainsclean.

After first-shot assembly 66 is placed in second-shot mold 110, asecond-shot of molding material is injected into second-shot mold 110 tosubstantially overmold the first-shot assembly 66 and create second-shotassembly 68 (134). In some examples, particular components ofsecond-shot assembly 68 may not be overmolded (e.g., may be kept free ofmolding material). For example, as described above, in some examples,electrode 42, distal end 53 of shaft 52, antenna coupling structure 58,and/or base 60 of attachment plate 46 may be kept clean and free ofmolding material.

FIG. 23 is a flow diagram illustrating an example technique for creatingheader 38 that includes creating a first-shot assembly with one or moreprotrusions extending outward from a substantially top portion of thefirst-shot assembly 66 and configured to guide flow of the second-shotmolding material during the second molding step along a surface of thefirst-shot assembly 66 toward a substantially bottom portion of thefirst-shot assembly 66 within second-shot mold 110. According to thetechnique of FIG. 23, pre-molding assembly 64 may be positioned withinfirst-shot mold 90 (136). In some examples, as described above withrespect to FIGS. 8-11, a loading fixture, e.g., loading fixture 82, maybe utilized to align and transfer pre-molding assembly 64 to first-shotmold 90.

In some examples, first-shot mold 90 may include divots 104 (FIGS. 14,15) configured to form protrusions 72A, 72B on first-shot assembly 66after the first molding step. Thus, positioning of pre-molding assembly64 within first-shot mold 90 may, in some examples, include aligningpre-molding assembly 64 within first-shot mold 90 such that divots 104are positioned proximate to a particular portion of pre-molding assembly64, e.g., proximate to a substantially top portion of pre-moldingassembly 64, such as proximate to antenna loading structure 58 andelectrode 42, in the examples described herein.

After positioning of pre-molding assembly 64 within first-shot mold 90,a first shot of molding material may be injected into first-shot mold 90to at least partially cover pre-molding assembly 64 and to createprotrusions 72A, 72B on a first portion or end of first-shot assembly 66(138). After the first-shot molding material has been cured and/orhardened, the first-shot assembly 66 may be removed from the first-shotmold and transferred to a second-shot mold 110. In some examples, thefirst-shot assembly 66 may be transferred to second-shot mold 110 via asecond loading fixture.

First-shot assembly 66 may subsequently be positioned within second-shotmold 110 (140). In some examples, as discussed above, first shotassembly 66 may be include protrusions 72A, 72B, which are located on asubstantially first end or portion of first-shot assembly 66, where theprotrusions 72A, 72B are configured to guide flow of a second-shotmolding material that is introduced proximate to the first portion orend of the first shot assembly in the second-shot mold 110. In suchexamples, when first shot assembly 66 is placed in the second shot mold,protrusions 72A, 72B may be located relatively close to an entry pointof molding material into a cavity of second-shot mold 110, in comparisonto other portions of second-shot mold 110. In this way, the moldingmaterial may contact protrusions 72A, 72B relatively early in itstransit through second-shot mold 110 and protrusions 72A, 72B may guideor direct flow of the molding material in a particular manner throughthe cavity of the second-shot mold from a first end or portion to asecond, different end or portion.

After first-shot assembly 66 is placed in second-shot mold 110, asecond-shot of molding material is injected into second-shot mold 110 tosubstantially overmold the first-shot assembly 66 and create second-shotassembly 68 (142). In some examples, particular components ofsecond-shot assembly 68 may not be overmolded (e.g., may be kept free ofmolding material). For example, as described above, in some examples,electrode 42, distal end 53 of shaft 52, antenna coupling structure 58,and/or base 60 of attachment plate 46 may be kept clean and free ofmolding material. As mentioned, protrusions 72A, 72B may be configuredto guide the second shot of molding material through the cavity ofsecond-shot mold 110 in a particular manner, e.g., by directing moldingmaterial through open regions 71 by guiding the molding material aroundthe top portion and down the side of first-shot assembly 66.

FIG. 24 is a flow diagram illustrating an example technique for couplingheader 38 to body 40 of IMD 16. Header 38 may, in some examples, beformed via the two step molding processes described herein. Header 38may be formed to include a header body portion that includes moldingmaterial and at least one component within the molding material. In someexamples, the header body portion may include some or all components ofheader 38 other than attachment plate 46. Header 38 may also be formedto include attachment plate 46 that includes base 60 defining space 65,and one or more extensions 62 defining one or more voids 63. Asdescribed above, voids 63 may be configured to receive molding materialto mechanically couple attachment plate 46 to the other components ofheader 38, e.g., to the header body.

According to the technique of FIG. 24, feedthrough wires 124 and/or 126may be positioned through a space defined within attachment plate 46 ofheader 38 (144). For example, as shown in FIG. 21, feedthrough wires 124and 126 may be positioned through space 65 defined within base 60 ofattachment plate 46 of header 38. In this way, feedthrough wires 124 and126, which may be electrically coupled to electrical components withinbody 40 (e.g., electrical circuitry 48 and/or power source 50), may beappropriately positioned to be coupled to components of header 38.Although the examples described herein include two feedthrough wires 124and 126, in other examples, IMD 16 may include any suitable number offeedthrough wires configured to electrically couple component(s) of body40 to component(s) of header 38.

According to the technique of FIG. 24, feedthrough wires 124 and/or 126may be electrically coupled to a component of header 38, e.g., electrode42 and/or antenna 44 of header 38 (146). For example, feedthrough wire124 may be electrically coupled to antenna coupling structure 56 ofantenna 44, in order to electrically couple components of body 40 of IMD16 (e.g., electrical circuitry 48 and/or power source 50) to antenna 44.As another example, feedthrough wire 126 may be electrically coupled todistal end 53 of shaft 52, which extends to electrode 42, in order toelectrically couple electrode 42 to components of body 40 of IMD 16(e.g., electrical circuitry 48 and/or power source 50). In this way, oneor more components of header 38 may be in electrical communication withcomponents of body 40.

According to the technique of FIG. 24, attachment plate 46 may bemechanically coupled to body 40 of IMD 16 (148). In this way, header 38and body 40 may be physically integrated to form IMD 16. Attachmentplate 46 may be mechanically coupled to body 40 in any suitable manner.For example, base 60 of attachment plate 46 may be laser welded to aportion of body 40, e.g., a portion of body 40 from which feedthroughwires 124 and 126 extend. In other examples, attachment plate 46 may bemechanically coupled to body 40 via another suitable technique.

Various examples have been described. These and other examples arewithin the scope of the following claims.

1. A method of forming a header for an implantable medical device, themethod comprising: positioning a pre-molding assembly within afirst-shot mold, wherein the pre-molding assembly comprises an antenna,an electrode, and an attachment plate, and wherein the first-shot molddefines at least one divot; and creating a first-shot assembly byintroducing a first shot molding material into the first-shot mold,wherein the first-shot assembly comprises the pre-molding assembly atleast partially covered by the first-shot molding material, wherein thefirst-shot assembly comprises at least one protrusion of the first shotmolding material extending from a surface of the first-shot assembly andformed by introduction of the first shot molding material into the atleast one divot of the first-shot mold.
 2. The method of claim 1,wherein the at least one protrusion extends from a surface of thefirst-shot assembly opposite the electrode, wherein the at least oneprotrusion is configured to engage with a wall of a second-shot mold tosubstantially prevent coverage of the electrode during injection of asecond shot molding material into the second-shot mold.
 3. The method ofclaim 2, wherein the at least one divot of the first-shot mold isadjacent to an antenna loading structure of the antenna, and wherein theat least one protrusion extends from a surface created by the antennaloading structure.
 4. The method of claim 2, further comprising placingthe first-shot assembly into the second-shot mold, wherein placing thefirst-shot assembly into the second-shot mold comprises placing the atleast one protrusion against a wall of the second-shot mold opposite theelectrode.
 5. The method of claim 1, wherein the at least one protrusionextends outward from a surface of the first-shot assembly at a firstportion of the first-shot assembly, wherein the at least one protrusionis configured to guide flow of a second-shot molding material introducedproximate to the first portion toward a second, different portion of thefirst-shot assembly within a second-shot mold.
 6. The method of claim 5,wherein the at least one protrusion extends between the electrode and anantenna loading structure of the antenna.
 7. The method of claim 5,further comprising placing the first-shot assembly into the second-shotmold, wherein placing the first-shot assembly into the second-shot moldcomprises placing the at least one protrusion proximate to a portion ofthe second-shot mold into which the second-shot molding material isintroduced.
 8. The method of claim 1, further comprising: placing thefirst-shot assembly into the second-shot mold; and injecting asecond-shot molding material into the second-shot mold to substantiallyovermold the first-shot assembly.
 9. A header for an implantable medicaldevice, the header comprising: a first-shot assembly comprising apre-molding assembly at least partially covered by a molding material,wherein the pre-molding assembly comprises an antenna, an electrode, andan attachment plate, wherein the first-shot assembly comprises at leastone protrusion of the first shot molding material extending from asurface of the first-shot assembly and formed by introduction of thefirst shot molding material into the at least one divot of thefirst-shot mold.
 10. The header of claim 9, wherein the at least oneprotrusion extends from a surface of the first-shot assembly oppositethe electrode, wherein the at least one protrusion is configured toengage with a wall of a second-shot mold to substantially preventcoverage of the electrode during injection of a second shot moldingmaterial into the second-shot mold.
 11. The header of claim 10, whereinthe at least one divot of the first-shot mold is adjacent to an antennaloading structure of the antenna, and wherein the at least oneprotrusion extends from a surface created by the antenna loadingstructure.
 12. The header of claim 9, wherein the at least oneprotrusion extends outward from a surface of the first-shot assembly ata first portion of the first-shot assembly, wherein the at least oneprotrusion is configured to guide flow of a second-shot molding materialintroduced proximate to the first portion toward a second, differentportion of the first-shot assembly within a second-shot mold.
 13. Theheader of claim 12, wherein the at least one protrusion extends betweenthe electrode and an antenna loading structure of the antenna.
 14. Theheader of claim 9, further comprising an overmold at least partiallycovering the first-shot assembly.
 15. The header of claim 9, wherein theattachment plate comprises at least one extension, wherein the at leastone extension defines at least one void filled with the moldingmaterial.
 16. The header of claim 9, wherein the attachment platecomprises a base configured to be mechanically coupled to a body of theimplantable medical device, wherein the base defines a space configuredto receive at least one feedthrough wire from the body of theimplantable medical device.